This disclosure relates generally to a method and apparatus for processing digital mammographic images.
Digital mammographic images or mammograms are usually presented as gray scale images having individual pixels, with each pixel having a pixel value corresponding to a specific gray scale value. These gray scale values may lie within a range of values between a minimum value of, for example, 0 (black) and a maximum value of, for example, 225 (white). The edge length of a typical mammogram is approximately 2000 to 4000 pixels, and the dissolution of a typical mammogram is approximately 10 line pairs/mm and/or 0.1 mm/pixel.
A mammographic imaging system may be coupled to a workstation, for example, a PACS (Picture Archiving and Communication System) workstation, on which a mammogram may be viewed and reviewed by a physician or other medical professionals. Mammography assigned PACS workstations usually have high resolution monitors, which are able to represent the high volume range and the comparatively high resolution of mammographic images.
Mammographic imaging systems generate raw mammograms containing measured data. These raw mammograms exhibit a global image characteristics with a comparatively high contrast in a boundary region of the measured object (i.e., the boundary region of the breast) and a relatively low contrast inside the measured object (i.e., the inside the breast). Conventional PACS workstations typically include tools for selecting parts of the whole gray scale level range and displaying these parts with maximum contrast through window level settings. Gray scale level ranges outside of the selected gray scale level window are mapped to the smallest or highest possible gray scale level, which means that information contained in these outside ranges is no longer displayed. Alternatively, nonlinear transfer functions represented through so called lookup tables may be applied to the raw mammogram modifying the global image characteristics in order to achieve a better over-all-contrast. Since the available total range of gray scale levels is fixed, a contrast enhancement for a selected part of the gray scale level range leads to a decrease of contrast in other gray level ranges. Therefore, an optimal display of all gray scale levels of the mammogram with optimal contrast and sharpness cannot be achieved by applying window level settings and/or lookup tables.
In order to evaluate the complete dynamic range of a mammogram, multiple window level settings and/or lookup tables are need to be applied, which would consecutively display the various gray scale level ranges, each in an optimal way. However, due to efficiency reasons, this can only be done in exceptional cases.
Most vendors sell their mammographic imaging systems with reviewing workstations that are able to perform processing of raw mammograms, based on the application of lookup tables. Additionally, vendors may include processing algorithms to reduce or remove the typical brightness decline along the breast edge or to increase local contrast in certain regions of the mammogram. The processing procedures of the various vendors may vary considerably in quality and overall impression of the generated images.
The users (physicians or other medical professionals) of these mammographic imaging systems may prefer to have standardized processing methods that work with all the different vendors and different imaging platforms including direct digital platforms, digitized film platforms, and computed radiography (CR) film platforms.
Therefore, there is a need for a method and apparatus for processing mammograms irrespective of the manufacturer of the mammographic imaging system in such a way that the processing improves contrast and sharpness without the necessity for using window level settings and/or lookup tables.